Technical Field
[0001] The invention generally relates to the field of mechanical locking of floorboards.
The invention relates to an improved locking system for mechanical locking of floorboards,
a floorboard provided with such an improved locking system, as well as a method for
making such floorboards. The invention generally relates to an improvement to a locking
system of the type described and shown in WO 9426999.
[0002] More specifically, the invention relates to a locking system for mechanical joining
of floorboards of the type having a body, opposite first and second joint edge portions
and a balancing layer on a rear side of the body, adjoining floorboards in a mechanically
joined position having their first and second joint edge portions joined at a vertical
joint plane, said locking system comprising
a) for vertical joining of the first joint edge portion of the first floorboard and
the second joint edge portion of the adjoining floorboard mechanically cooperating
means in the form of a tongue groove formed in the first joint edge portion and a
tongue formed in the second joint edge portion,
b) for horizontal joining of the first joint edge portion of the first floorboard
and the second joint edge portion of an adjoining floorboard mechanically cooperating
means, which comprise
a locking groove which is formed in the underside of said second floorboard and
which extends parallel to and at a distance from the vertical joint plane at said
second joint edge portion and which has a downward opening, and
a strip made in one piece with the body of said first floorboard, which strip at
said first joint edge portion projects from said vertical joint plane and at a distance
from the joint plane has a locking element, which projects towards a plane containing
the upper side of said first floorboard and which has at least one operative locking
surface for coaction with said locking groove, and
said strip forming a horizontal extension of the first joint edge port-ion below
the tongue groove.
Field of Application of the Invention
[0003] The present invention is particularly suitable for mechanical joining of thin floating
floorboards made up of an upper surface layer, an intermediate fibreboard body and
a lower balancing layer, such as laminate flooring and veneer flooring with a fibreboard
body. Therefore, the following description of the state of the art, problems associated
with known systems, and the objects and features of the invention will, as a non-restricting
example, focus on this field of application and, in particular, on rectangular floorboards
with dimensions of about 1.2 m * 0.2 m and a thickness of about 7-10 mm, intended
to be mechanically joined at the long side as well as the short side.
Background of the Invention
[0004] Thin laminate flooring and wood veneer flooring are usually composed of a body consisting
of a 6-9 mm fibreboard, a 0.2-0.8-mm-thick upper surface layer and a 0.1-0.6 mm lower
balancing layer. The surface layer provides appearance and durability to the floorboards.
The body provides stability, and the balancing layer keeps the board level when the
relative humidity (RH) varies during the year. The RH can vary between 15% and 90%.
Conventional floorboards of this type are usually joined by means of glued tongue-and-groove
joints at the long and short sides. When laying the floor, the boards are brought
together horizontally, whereby a projecting tongue along the joint edge of a first
board is introduced into the tongue groove along the joint edge of a second board.
The same method is used on both the long and the short side. The tongue and the tongue
groove are designed for such horizontal joining only and with special regard to how
the glue pockets and gluing surfaces should be designed to enable the tongue to be
efficiently glued within the tongue groove. The tongue-and-groove joint presents coacting
upper and lower contact surfaces that position the boards vertically in order to ensure
a level surface of the finished floor.
[0005] In addition to such conventional floors which are connected by means of glued tongue-and-groove
joints, floorboards have recently been developed which are instead mechanically joined
and which do not require the use of glue. This type of a mechanical joint system is
hereinafter referred to as a "strip-lock system" since the most characteristic component
of this system is a projecting strip which supports a locking element.
[0006] WO 9426999 (Applicant Välinge Aluminium AB) discloses a strip-lock system for joining
building panels, particularly floorboards. This locking system allows the boards to
be locked mechanically at right angles to as well parallel to the principal plane
of the boards at the long side as well as at the short side. Methods for making such
floorboards are disclosed in WO 9824994 and WO 9824995. The basic principles of the
design and the installation of the floorboards, as well as the methods for making
the same, as described in the three above-mentioned documents are usable for the present
invention as well, and, therefore, these documents are hereby incorporated by reference.
[0007] In order to facilitate the understanding and description of the present invention,
as well as the comprehension of the problems underlying the invention, a brief description
of the basic design and function of the floorboards according to the above-mentioned
WO 9426999 will be given below with reference to Figs 1-3 in the accompanying drawings.
Where applicable, the following description of the prior art also applies to the embodiments
of the present invention described below.
[0008] Figs 3a and 3b are thus a bottom view and a top view respectively of a known floorboard
1. The board 1 is rectangular with a top side 2, an underside 3, two opposite long
sides 4a, 4b forming joint edges, and two opposite short sides 5a, 5b forming joint
edges.
[0009] Without the use of glue, both the long sides 4a, 4b and the short sides 5a, 5b can
be joined mechanically in a direction D2 in Fig. 1c. For this purpose, the board 1
has a flat strip 6, mounted at the factory, projecting horizontally from its long
side 4a, which strip extends throughout the length of the long side 4a and which is
made of flexible, resilient sheet aluminium. The strip 6 can be fixed mechanically
according to the embodiment shown, or by means of glue, or in some other way. Other
strip materials can be used, such as sheets of other metals, as well as aluminium
or plastic sections. Alternatively, the strip 6 may be made in one piece with the
board 1, for example by suitable working of the body of the board 1. Thus, the present
invention is usable for floorboards in which the strip is integrally formed with the
board. At any rate, the strip 6 should always be integrated with the board 1, i.e.
it should never be mounted on the board 1 in connection with the laying of the floor.
The strip 6 can have a width of about 30 mm and a thickness of about 0.5 mm. A similar,
but shorter strip 6' is provided along one short side 5a of the board 1. The edge
side of the strip 4 facing away from the joint edge 4a is formed with a locking element
8 extending throughout the length of the strip 6. The locking element 8 has an operative
locking surface 10 facing the joint edge 4a and having a height of e.g. 0.5 mm. When
the floor is being laid, this locking surface 10 coacts with a locking groove 14 formed
in the underside 3 of the opposite long side 4b of an adjoining board 1'. The short
side strip 6' is provided with a corresponding locking element 8', and the opposite
short side 5b has a corresponding locking groove 14'.
[0010] Moreover, for mechanical joining of both the long sides and the short sides also
in the vertical direction (direction D1 in Fig. 1c), the board 1 is formed with a
laterally open recess 16 along one long side 4a and one short side 5a. At the bottom,
the recess is defined by the respective strips 6, 6' . At the opposite edges 4b and
5b, there is an upper recess 18 defining a locking tongue 20 coacting with the recess
16 (see Fig. 2a).
[0011] Figs 1a-1c show how two long sides 4a, 4b of two such boards 1, 1' on an underlay
U can be joined together by means of downward angling. Figs 2a-2c show how the short
sides 5a, 5b of the boards 1, 1' can be joined together by snap action. The long sides
4a, 4b can be joined together by means of both methods, while the short sides 5a,
5b - when the first row has been laid - are normally joined together subsequent to
joining together the long sides 4a, 4b and by means of snap action only.
[0012] When a new board 1' and a previously installed board 1 are to be joined together
along their long sides 4a, 4b as shown in Figs 1a-1c, the long side 4b of the new
board 1' is pressed against the long side 4a of the previous board 1 as shown in Fig.
1a, so that the locking tongue 20 is introduced into the recess 16. The board 1' is
then angled downwards towards the subfloor 12 as shown in Fig. 1b. In this connection,
the locking tongue 20 enters the recess 16 completely, while the locking element 8
of the strip 6 enters the locking groove 14. During this downward angling the upper
part 9 of the locking member 8 can be operative and provide guiding of the new board
1' towards the previously installed board 1. In the joined position as shown in Fig.
1c, the boards 1, 1' are locked in both the direction D1 and the direction D2 along
their long sides 4a, 4b, but can be mutually displaced in the longitudinal direction
of the joint along the long sides 4a, 4b.
[0013] Figs 2a-2c show how the short sides 5a and 5b of the boards 1, 1' can be mechanically
joined in the direction D1 as well as the direction D2 by moving the new board 1'
towards the previously installed board 1 essentially horizontally. Specifically, this
can be carried out subsequent to joining the long side of the new board 1' to a previously
installed board in an adjoining row by means of the method according to Figs 1a-1c.
In the first step in Fig. 2a, bevelled surfaces adjacent to the recess 16 and the
locking tongue 20 respectively co-operate such that the strip 6' is forced to move
downwards as a direct result of the bringing together of the short sides 5a, 5b. During
the final urging together of the short sides, the strip 6' snaps up when the locking
element 8' enters the locking groove 14'.
[0014] By repeating the steps shown in Figs 1a-c and 2a-c, the whole floor can be laid without
the use of glue and along all joint edges. Known floorboards of the above-mentioned
type are thus mechanically joined usually by first angling them downwards on the long
side, and when the long side has been secured, snapping the short sides together by
means of horizontal displacement along the long side. The boards 1, 1' can be taken
up in the reverse order of laying without causing any damage to the joint, and be
laid again. These laying principles are also applicable to the present invention.
[0015] For optimal function, subsequent to being joined together, the boards should be capable
of assuming a position along their long sides in which a small play can exist between
the locking surface 10 and the locking groove 14. Reference is made to WO 9426999
for a more detailed description of this play.
[0016] In addition to what is known from the above-mentioned patent specifications, a licensee
of Välinge Aluminium AB, Norske Skog Flooring AS (NSF), introduced a laminated floor
with mechanical joining according to WO 9426999 in January 1996 in connection with
the Domotex trade fair in Hannover, Germany. This laminated floor, which is marketed
under the brand name Alloc®, is 7.2 mm thick and has a 0.6-mm aluminium strip 6 which
is mechanically attached on the tongue side. The operative locking surface 10 of the
locking element 8 has an inclination (hereinafter termed locking angle) of 80° to
the plane of the board. The vertical connection is designed as a modified tongue-and-groove
joint, the term "modified" referring to the possibility of bringing the tongue and
tongue groove together by way of angling.
[0017] WO 9747834 (Applicant Unilin) describes a strip-lock system which has a fibreboard
strip and is essentially based on the above known principles. In the corresponding
product, "Uniclic", which this applicant began marketing in the latter part of 1997,
one seeks to achieve biasing of the boards. This results in high friction and makes
it difficult to angle the boards together and to displace them. The document shows
several embodiments of the locking system. The "Uniclic" product, shown in section
in Fig. 4b, consists of a floorboard having a thickness of 8.1 mm with a strip having
a width of 5.8 mm, comprising an upper part made of fibreboard and a lower part composed
of the balancing layer of the floorboard. The strip has a locking element 0.7 mm in
height with a locking angle of 45°. The vertical connection consists of a tongue and
a tongue groove having a tongue groove depth of 4.2 mm.
[0018] Other known locking systems for mechanical joining of board materials are described
in, for example, GB-A-2,256,023 showing unilateral mechanical joining for providing
an expansion joint in a wood panel for outdoor use, and in US-A-4,426,820 showing
a mechanical locking system for plastic sports floors, which floor however does not
permit displacement and locking of the short sides by snap action. In both these known
locking systems the boards are uniform and do not have a separate surface layer and
balancing layer.
[0019] In the autumn of 1998, NSF introduced a 7.2-mm laminated floor with a strip-lock
system which comprises a fibreboard strip and is manufactured in accordance with WO
9426999. This laminated floor, which is shown in cross-section in Fig. 4a, is marketed
under the brand name of "Fiboloc®". In this case, too, the strip comprises an upper
part of fibreboard and a lower part composed of a balancing layer. The strip is 10.0
mm wide, the height of the locking element is 1.3 mm and the locking angle is 60°.
The depth of the tongue groove is 3.0 mm.
[0020] In January 1999, Kronotex introduced a 7.8 mm thick laminated floor with a strip
lock under the brand name "Isilock". This system is shown in cross-section in Fig.
4c. In this floor, too, the strip is composed of fibreboard and a balancing layer.
The strip is 4.0 mm and the tongue groove depth is 3.6 mm. "Isilock" has two locking
ridges having a height of 0.3 mm and with locking angles of 40°. The locking system
has low ten-sile strength, and the floor is difficult to install.
Summary of the Invention
[0021] Although the floor according to WO 9426999 and the. floor sold under the brand name
Fiboloc® exhibit major advantages in comparison with traditional, glued floors, further
improvements are desirable mainly by way of cost savings which can be achieved by
reducing the width of the fibreboard strip from the present 10 mm. A narrower strip
has the advantage of producing less material waste in connection with the forming
of the strip. However, this has not been possible since narrower strips of the Uniclic
and Isilock type have produced inferior test results. The reason for this is that
narrow strips require a small angle of the locking surface of the locking element
in relation to the horizontal plane (termed locking angle) in order to enable the
boards to be joined together by means of angling, since the locking groove follows
an arc having its centre in the upper joint edge of the board. The height of the locking
element must also be reduced since narrow strips are not as flexible, rendering snap
action more difficult.
[0022] To sum up, narrow strips have the advantage that material waste is reduced, but the
drawbacks that the locking angle must be small to permit angling and that the locking
element must be low to permit joining by snap action.
[0023] \ In repeated laying trials and tests with the same batch of floorboards we have
discovered that strip locks, which have a joint geometry similar to that in Figs 4b
and 4c, and are composed of a narrow fibreboard strip with a balancing layer on its
rear side and with a locking element having a small locking surface with a low locking
angle, exhibit a considerable number of properties which are not constant and which
can vary substantially in the same floorboard at different points in time when laying
trials have been performed. These problems and the reason behind the problems are
not known.
[0024] Moreover, at present there are no known products or methods which afford adequate
solutions to these problems which are related to
(i) mechanical strength of the joint of floorboards with a mechanical locking system
of the strip lock type;
(ii) handling and laying of such floorboards;
(iii) properties of a finished, joined floor made of such floorboards.
(i) Strength
[0025] At a certain point in time, the joint system of the floorboards has adequate strength.
In repeated testing at a different point in time, the strength of the same floorboard
may be considerably lower, and the locking element slides out of the locking groove
relatively easily when the floor is subjected to tensile stress transversely of the
joint.
(ii) Handling/Laying
[0026] At certain times during the year the boards can be joined together, while at other
times it is very difficult to join the same floorboard. There is a considerable risk
of damage to the joint system in the form of cracking.
(iii) Properties of the Joined Floor
[0027] The quality of the joint in the form of the gap between the upper joint edges of
the floorboards when subjected to stress varies for the same floorboard at different
times during the year.
[0028] It is known that floorboards expand and shrink during the year when the relative
humidity RH changes. Expansion and shrinking are 10 times greater transversely of
the direction of the fibres than in the direction of the fibres. Since both joint
edges of the joint system change by the same amount essentially simultaneously, the
expansion and the shrinking cannot explain the undesirable effects which severely
limit the chances of providing a strip-lock system at a low cost which at the same
time is of high quality with respect to strength, laying properties, and the quality
of the joint. According to generally known theories, wide strips should expand more
and cause greater problems. Our tests indicate that the reverse is the case.
[0029] In sum, there is a great need for a strip-lock system which to a greater extent than
the prior art takes into account the above-mentioned requirements, problems and wishes.
It is an object of the invention to fulfil this need.
[0030] These and other objects of the invention are achieved by a locking system, a floorboard,
and a manufacturing method exhibiting the properties stated in the appended independent
claims, preferred embodiments being stated in the dependent claims.
[0031] The invention is based on a first insight according to which the problems identified
are essentially connected to the fact that the strip which is integrated with the
body bends upwards and downwards when the RH changes. Moreover, the invention is based
on the insight that, as a result of its design, the strip is unbalanced and acts as
a bimetal. When, in a decrease of the RH, the rear balancing layer of the strip shrinks
more than the fibreboard part of the strip, the entire strip will bend backwards,
i.e. downwards. Such strip-bending can be as great as about 0.2 mm. A locking element
having a small operative locking surface, e.g. 0.5 mm, and a low locking angle, e.g.
45 degrees, will then cause a play in the upper part of the horizontal locking system,
which means that the locking element of the strip easily slides out of the locking
groove. If the strip is straight or slopes upward it will be extremely difficult to
lay the floor if the locking system is adapted to a curved strip.
[0032] One reason why the problem is difficult to solve is that the deflection of the strip
is not known when the floor is being laid or when it has been taken up and is being
laid again, which is one of the major advantages of the strip lock in comparison with
glued joints. Consequently, it is not possible to solve the problem by adapting in
advance the working measurements of the strip and/or the locking groove to the curvature
of the strip, since the latter is unknown.
[0033] Nor is it preferred to solve this problem by using a wide strip, whose locking element
has a higher locking surface with a larger locking angle, since a wide strip has the
drawback of considerable material wastage in connection with the forming of the strip.
The reason why the wider but more costly strip works better is mainly because the
locking surface is substantially larger than the maximum strip bending and because
the high locking angle only causes a marginally greater play which is not visible.
[0034] The strip-bending problems are reinforced by the fact that laminate flooring is subjected
to unilateral moisture influence. The surface layer and the balancing layer do not
co-operate fully, and this always gives rise to a certain amount of bulging. Concave
upward bulging is the biggest problem, since this causes the joint edges to rise.
The result is an undesirable joint opening between the boards in the upper side of
the boards and high wear of the joint edges. Accordingly, it is desirable to provide
a floorboard which in normal relative humidity is somewhat upwardly convex by biasing
the rear balancing layer. In traditional, glued floors this biasing is not a problem,
rather, it creates a desirable advantage. However, in a mechanically joined floor
with an integrated strip lock the biasing of the balancing layer results in an undesirable
drawback since the bias reinforces the imbalance of the strip and, consequently, causes
a greater, undesirable backward bending of the strip. This problem is difficult to
solve since the bias is an inherent quality of the balancing layer, and, consequently,
cannot be eliminated from the balancing layer.
[0035] The invention is also based on a second insight which is related to the geometry
of the joint. We have also discovered that a strip lock with a relatively deep tongue
groove gives rise to greater undesirable bending of the strip. The reason behind this
phenomenon is that the tongue groove, too, is unbalanced. Consequently, the tongue
groove opens when, in a decrease of the RH, the balancing layer shrinks to a greater
extent than the fibreboard part of the strip, causing the strip to bend downwards
since the strip is an extension of the joint edge below the tongue groove.
[0036] According to a first aspect of the invention a locking system is provided of the
type which is stated in the first paragraph but one of the description and which,
according to the invention, is characterised in that the second joint edge, within
an area (P) defined by the bottom of the tongue groove and the locking surface of
the locking element, is modified with respect to the balancing layer.
[0037] Said area P, which is thus defined by the bottom of the tongue groove and the locking
surface of the locking element, is the area which is sensitive to bending. If the
strip bends within this area P, the position of the locking surface relative to the
locking groove, and thus the properties of the joint, will be affected. Especially,
it should be noted that this entire area P is unbalanced, since nowhere does the part
of the balancing layer located in this area P have a coacting, balancing surface layer,
neither in the tongue groove nor on the projecting strip. According to the invention,
by modifying the balancing layer within this area P it is possible to change this
unbalanced state in a positive direction, such that the undesirable strip-bending
is reduced or eliminated.
[0038] The term "modified" refers to both (i) a preferred embodiment in which the balancing
layer has been modified "over time", i.e. the balancing layer has first been applied
across the entire area P during the manufacturing process, but has then been subjected
to modifying treatment, such as milling or grooving and/or chemical working, and (ii)
variants in which the balancing layer at least across part of the area P has been
modified "in space", i.e. that the area P differs from the rest of the board with
respect to the appearance/properties/structure of the balancing layer.
[0039] The balancing layer can be modified across the entire horizontal extent of the area
P, or within only one or several parts thereof. The balancing layer can also be modified
under the whole of the locking element or parts thereof. However, it may be preferable
to keep the balancing layer intact under at least part of the locking element to provide
support for the strip against the underlay.
[0040] According to a preferred embodiment, "modifying" means that the balancing layer is
completely or partially removed. In one embodiment, the whole area P lacks a balancing
layer.
[0041] In a second embodiment, there is no balancing layer at all within one or several
parts of the area P. Depending on the type of balancing layer and the geometry of
the joint system, it is, for example, possible to keep the whole balancing layer or
parts thereof under the tongue groove.
[0042] In a third embodiment, the balancing layer is not removed completely; it is only
reduced in thickness. The latter embodiment can be combined with the former ones.
There are balancing layers where the main problems can be eliminated by partial removal
of some layers only. The rest of the balancing layer can be retained and helps to
increase the strength and flexibility of the strip. Balancing layers can also be specially
designed with different layers which are adapted in such a way that they both balance
the surface and can act as a support for the strip when parts of the layers are removed
within one area of the rear side of the strip.
[0043] The modification can also mean a change in the material composition and/or material
properties of the balancing layer.
[0044] Preferably, the modification can be achieved by means of machining such as milling
and/or grinding but it could also be achieved by means of chemical working, heat treatment
or other methods which remove material or change material properties.
[0045] The invention also provides a manufacturing method for making a moisture-stable strip-lock
system. The method according to the invention comprises the steps of forming each
floorboard from a body,
providing the rear side of the body with a balancing layer,
forming the floorboard with first and second joint edge portions,
forming said first joint edge portion with
a first joint edge surface portion extended from the upper side of the floorboard
and defining a joint plane along said first joint edge portion,
a tongue groove which extends into the body from said joint plane,
a strip formed from the body and projecting from said joint plane and supporting
at a distance from this joint plane an upwardly projecting locking element with a
locking surface facing said joint plane,
forming said second joint edge portion with
a second joint edge surface portion extended from the upper side of the floorboard
and defining a joint plane along said second joint edge portion,
a tongue projecting from said joint plane for coaction with a tongue groove of
the first joint edge portion of an adjoining floorboard, and
a locking groove which extends parallel to and at a distance from the joint plane
of said second joint edge portion and which has a downward opening and is designed
to receive the locking element and cooperate with said locking surface of the locking
element.
[0046] The method according to the invention is characterised by the step of working the
balancing layer within an area defined by the bottom of the tongue groove and the
locking surface of the locking element.
[0047] The adaptation or removal of part of the balancing layer in the joint system can
be carried out in connection with the gluing/lamination of the surface layer, the
body, and the balancing layer by displacing the balancing layer relative to the surface
layer. It is also possible to carry out modifications in connection with the manufacture
of the balancing layer so that the part which will be located adjacent to the locking
system will have properties which are different from those of the rest of the balancing
layer.
[0048] However, a very suitable manufacturing method is machining by means of milling or
grinding. This can be carried out in connection with the manufacture of the joint
system and the floorboards can be glued/laminated in large batches consisting of 12
or more floorboards.
[0049] The strip-lock system is preferably manufactured using the upper floor surface as
a reference point. The thickness tolerances o f the floorboards result in strips of
unequal thickness since there is always a,predetermined measurement from the top side
of the strip to the floor. Such a manufacturing method results in tongue grooves of
different depths in the rear side and a partial removal of a thin balancing layer
cannot be performed in a controlled manner. The removal of the balancing layer should
thus be carried out using the rear side of the floorboard as a reference surface instead.
[0050] It has also been an object to provide a cost-optimal joint which is also of high-quality
by making the strip as narrow as possible and the tongue groove as shallow and as
strong as possible in order both to reduce waste since the tongue can be made narrow
and to eliminate as far as possible the situation where the tongue groove opens up
and causes strip-bending as well as rising of the upper joint edge when the relative
humidity changes.
[0051] Known strip-lock systems with a strip of fibreboard and a balancing layer are characterised
in that the shallowest known tongue groove is 3.0 mm in a 7.2-mm-thick floorboard.
The depth of the tongue groove is thus 0.42 times the thickness of the floor. This
is only known in combination with a 10.0-mm-wide strip which thus has a width which
is 1.39 times the floor thickness. All other such known strip joints with narrow strips
have a tongue groove depth exceeding 3.6 mm and this contributes considerably to the
strip-bending.
[0052] In order to fulfil the above-mentioned object a strip-lock system is provided which
is characterised in that the tongue groove depth of the tongue groove and the width
of the strip are less than 0.4 and 1.3 times the floor thickness respectively. This
joint affords good joint properties and especially in combination with high rigidity
of the tongue groove since it can be designed in such a way that as much material
as possible is retained between the upper part of the tongue groove and the floor
surface as well as between the lower part of tongue groove and the rear side of the
floor while, at the same time, it is possible to eliminate the strip-bending problems
as described above. This strip-lock system can be combined with one or more of the
preferred embodiments which are disclosed in connection with the solution based on
a modification of the balancing layer.
[0053] The opposite joint edge of the board is also unbalanced. In this case, the problems
are not nearly as serious since the surface layer is not biased and the unbalanced
part is more rigid. However, in this case, too, an improvement can be achieved by
making the strip as thin as possible. This permits minimal removal of material in
the locking groove part of the joint system, which in turn results in maximum rigidity
in this unbalanced part.
[0054] According to the invention there is thus provided a strip-lock system having a joint
geometry characterised in that there is a predetermined relationship between the width
and thickness of the strip and the height of the locking element on the one hand and
the floor thickness on the other. Furthermore, there is provided a minimum locking
angle for the locking surface. All these parameters separately and in combination
with each other and the above inventions contribute to the creation of a strip-lock
system which can have high joint quality and which can be manufactured at a low cost.
Brief Description of the Drawings
[0055] Figs 1a-c show in three stages a downward angling method for mechanical joining of
long sides of floorboards according to WO 9426999.
[0056] Figs 2a-c show in three stages a snap-action method for mechanical joining of short
sides of floorboards according to WO 9426999.
[0057] Figs 3a and 3b are a top view and a bottom view respectively of a floorboard according
to WO 9426999.
[0058] Fig. 4 shows three strip-lock systems available on the market with an integrated
strip of fibreboard and a balancing layer.
[0059] Fig. 5 shows a strip lock with a small tongue groove depth and with a wide fibreboard
strip, which supports a locking element having a large locking surface and a high
locking angle.
[0060] Fig. 6 shows a strip lock with a large tongue groove depth and with a narrow fibreboard
strip, which supports a locking element having a small locking surface and a low locking
angle.
[0061] Figs 7 and 8 illustrate strip-bending in a strip lock according to Fig. 5 and Fig.
6.
[0062] Fig. 9 shows the joint edges of a floorboard according to an embodiment of the invention.
[0063] Figs 10 and 11 show the joining of two floorboards according to Fig. 9.
[0064] Figs 12 and 13 show two alternative embodiments of the invention.
Description of Preferred Embodiments
[0065] Prior to the description of preferred embodiments, with reference to Figs 5-8, a
detailed explanation will first be given of the background to and the impact of strip-bending.
[0066] The cross-sections shown in Figs 5 and 6 are hypothetical, unpublished cross-sections,
but they are fairly similar to "Fiboloc®" in Fig. 4a and "Uniclic" in Fig. 4b. Accordingly,
Figs 5 and 6 do not represent the invention. Parts which correspond to those in the
previous Figures are in most cases provided with the same reference numerals. The
design, function, and material composition of the basic components of the boards in
Figs 5 and 6 are essentially the same as in embodiments of the present invention and,
consequently, where applicable, the following description of Figs 5 and 6 also applies
to the subsequently described embodiments of the invention.
[0067] In the embodiment shown, the floorboards 1, 1' in Fig. 5 are rectangular with opposite
long sides, 4a, 4b and opposite short sides 5a, 5b. Fig. 5 shows a vertical cross-section
of a part of a long side 4a of the board 1, as well as a part of a long side 4b of
an adjoining board 1'. The body of the board 1 can be composed of a fibreboard body
30, which supports a surface layer 32 on its front side and a balancing layer 34 on
its rear side. A strip 6 formed from the body and the balancing layer of the floorboard
and supporting a locking element 8 constitutes an extension of the lower tongue groove
part 36 of the floorboard 1. The strip 6 is formed with a locking element 8, whose
operative locking surface 10 cooperates with a locking groove 14 in the opposite joint
edge 4b of the adjoining board 1' for horizontal locking of the boards 1, 1' transversely
of the joint edge (D2). The locking element 8 has a relatively large height LH and
a high locking angle A. The upper part of the locking element has a guiding part 9
which guides the floorboard to the correct position in connection with angling. The
locking groove 14 has a larger width than the locking element 8, as is evident from
the Figures.
[0068] For the purpose of forming a vertical lock in the direction D1, the joint edge portion
4a exhibits a laterally open tongue groove 36 and the opposite joint edge portion
4b exhibits a tongue 38 which projects laterally from a joint plane F and which in
the joined position is received in the tongue groove 36.
[0069] In the joined position according to Fig. 5, the two adjoining, upper joint edge surface
portions 41 and 42 of the boards 1, 1' define this vertical joint plane F.
[0070] The strip 6 has a horizontal extent W (= strip width) which can be divided into:
(a) an inner part with a horizontal extent D (locking distance) which is defined by
the joint plane F and a vertical line through the lower part of the locking surface
10, as well as (b) an outer part with a horizontal extent L (the width of the locking
element). The tongue groove 36 has a horizontal tongue groove depth G measured from
the joint plane F and inwards towards the board 1 to a vertical limiting plane which
coincides with the bottom of the tongue groove 36. The tongue groove depth G and the
extent D of the locking distance together form a joint part within an area P consisting
of components forming part of the vertical lock D1 and the horizontal lock D2.
[0071] Fig. 6 shows an embodiment which is different from the embodiment in Fig. 5 in that
the tongue groove depth G is greater, and the strip width W, the height LH, and the
locking angle A of the locking surface are all smaller. However, the size of the area
P is the same in the embodiments in Figs 5 and 6.
[0072] Reference is now made to Figs 7 and 8, which show strip-bending in the embodiments
in Figs 5 and 6 respectively. The relevant part of the curvature which may cause problems
is the area P, since a curvature in the area P results in a change of position of
the locking surface 10. Since the area P has the same horizontal extent in both embodiments,
all else being equal, the strip-bending at the locking surface 10 will be of the same
magnitude despite the fact that the strip length W is different.
[0073] The large locking surface 10 and the large locking angle A in Fig. 5 will not cause
any major problems in Fig. 7, since the greater part of the locking surface 10 is
still operative. The high locking angle A contributes only marginally to increased
play between the locking element 8 and the locking groove 14. In Fig. 8, however,
the large tongue groove depth G as well as the small locking surface 10 and the low
locking angle A2 create major problems. The strength of the locking system is considerably
reduced and the play between the locking element 8 and the locking groove 14 increases
substantially and causes joint openings in connection with tensile stress. If the
play of the boards is adapted to a sloping strip at the time of manufacture it may
prove impossible to lay the boards if the strip 6 is flat or bent upwards.
[0074] We have realised that the strip-bending is a result of the fact that the joint part
P is unbalanced and that the shape changes in the balancing layer 34 and the fibreboard
part 30 of the strip are not the same when the relative humidity changes. In addition,
the bias of the balancing layer 34 contributes to bending the strip 6 backwards/downwards.
[0075] The deciding factors of the strip-bending are the extent of the locking distance
D and the tongue groove depth G. The appearance of the tongue groove 36 and the strip
6 also has some importance. A great deal of material in the joint portion P makes
the tongue groove and the strip more rigid and counteracts strip-bending.
[0076] Figs 9-11 show how a cost-efficient strip-lock system with a high quality joint can
be designed according to the invention. Fig. 9 shows a vertical cross-section of the
whole board 1 seen from the short side, with the main portion of the board broken
away. Fig. 10 shows two such boards 1, 1' joined at the long sides 4a, 4b. Fig. 11
shows how the long sides can be angled together in connection with laying and angled
upward when being taken up. The short sides can be of the same shape.
[0077] In connection with the manufacture of the strip-lock system, the balancing layer
34 has been milled off both in the entire area G under the tongue groove 36 and across
the entire rear side of the strip 6 across the width W (including the area L under
the locking element 8). The modification according to the invention in the form of
removal of the balancing layer 34 in the whole area P eliminates both the bias and
the strip-bending resulting from moisture movement.
[0078] In order to save on materials, in this embodiment the width W of the strip 6 has
been reduced as much as possible to a value which is less than 1.3 times the floor
thickness.
[0079] The tongue groove depth G of the tongue groove 36 has also been limited as much as
possible both to counteract undesirable strip-bending and to save on materials. In
its lower part, the tongue groove 36 has been given an oblique part 45 in order to
make the tongue groove 36 and the joint portion P more rigid.
[0080] In order to counteract the effect of the strip-bending and to comply with the strength
requirements, the locking surface has a minimum inclination of at least 45 degrees
and the height of the locking element exceeds 0.1 times the floor thickness T.
[0081] In order to make the locking-groove part of the joint system as stable as possible,
the thickness SH of the strip in an area corresponding to at least half the locking
distance D has been limited to a maximum of 0.25 times the floor thickness T. The
height LH of the locking element has been limited to 0.2 times the floor thickness
and this means that the locking groove 14 can be formed by removing a relatively small
amount of material.
[0082] In more basic embodiments of the invention, only the measure "modification of balancing
layer" is used.
[0083] Fig. 12 shows an alternative embodiment for eliminating undesirable strip-bending.
Here, the balancing layer 34 has been completely removed within the area P (including
area G under the tongue groove). However, under the locking element 8 in the area
L the balancing layer is intact in the form of a remaining area 34', which advantageously
constitutes a support for the locking element 8 against the subfloor. Since the remaining
part 34' of the balancing layer is located outside the locking surface 10 it only
has a marginal, if any, negative impact on the change of position of the locking surface
10 in connection with strip-bending and thus changes in moisture content.
[0084] Within the scope of the invention there are a number of alternative ways of reducing
strip-bending. For example, several grooves of different depths and widths can be
formed in the balancing layer within the entire area P and L. Such grooves could be
completely or partially filled with materials which have properties that are different
from those of the balancing layer 34 of the floorboard and which can contribute to
changes in the properties of the strip 6 with respect to, for example, flexibility
and tensile strength. Filling materials with fairly similar properties can also be
used when the objective is to essentially eliminate the bias of the balancing layer.
[0085] Complete or partial removal of the balancing layer P in the area P and refilling
with suitable bonding agents, plastic materials, or the like can be a way of improving
the properties of the strip 6.
[0086] Fig. 13 shows an embodiment in which only part of the outer layer of the balancing
layer has been removed across the entire area P. The remaining, thinner part of the
balancing layer is designated 34". The part 34' has been left intact under the locking
element 8 in the area L. The advantage of such an embodiment is that it may be possible
to eliminate the major part of the strip-bending while a part (34") of the balancing
layer is kept as a reinforcing layer for the strip 6. This embodiment is particularly
suitable when the balancing layer 34 is composed of different layers with different
properties. The outer layer can, for example, be made of melamine and decoration paper
while the inner layer can be made of phenol and Kraft paper. Various plastic materials
can also be used with various types of fibre reinforcement. Partial removal of layers
can, of course, be combined with one or more grooves of different depths and widths
under the entire joint system P + L. The working from the rear side can also be adapted
in order to increase the flexibility of the strip in connection with angling and snap
action.
[0087] Two main principles for reducing or eliminating strip-bending have now been described
namely: (a) modifying the balancing layer within the entire area P or parts thereof,
and (b) modifying the joint geometry itself with a reduced tongue groove depth and
a special design of the inner part of the tongue groove in combination. These two
main principles are usable separately to reduce the strip-bending problem, but preferably
in combination.
[0088] According to the invention, these two basic principles can also be combined with
further modifications of the joint geometry (c) which are characterised in that:
- The strip is made narrow preferably less than 1.3 times the floor thickness;
- The inclination of the locking surface is at least 45 degrees;
- The height of the locking element exceeds 0.1 times the floor thickness and is less
than 0.2 times the floor thickness;
- The strip is designed so that at least half the locking distance has a thickness which
is less than 0.25 times the floor thickness.
[0089] The above embodiments separately and in combination with each other and the above
main principles contribute to the provision of a strip-lock system which can be manufactured
at a low cost and which at the same affords a high quality joint with respect to laying
properties, disassembly options, strength, joint opening, and stability over time
and in different environments.
[0090] Several variants of the invention are possible. The joint system can be made in a
number of different joint geometry where some or all of the above parameters are different,
particularly when the purpose is to give precedence to a certain property over the
others.
[0091] Applicant has considered and tested a large number of variants in the light of the
above: "smaller" can be changed to "larger", relationships can be changed, other radii
and angles can be chosen, the joint system on the long side and the short side can
be made different, two types of boards can be made where, for example, one type has
a strip on both opposite sides while the other type has a locking groove on the corresponding
sides, boards can be made with strip locks on one side and a traditional glued joint
on the other, the strip-lock system can be designed with parameters which are generally
intended to facilitate laying by positioning the floorboards and keeping them together
until the glue hardens, and different materials can be sprayed on the joint system
to provide impregnation against moisture, reinforcement, or moisture-proofing, etc.
In addition, there can be mechanical devices, changes in the joint geometry and/or
chemical additives such as glue which are aimed at preventing or impeding, for example,
a certain type of laying (angling or snap action), displacement in the direction of
the joint, or a certain way of taking up the floor, for example, upward angling or
pulling along the joint edge.
[0092] Specific embodiments of the disclosure are set forth in the following numbered clauses.
1. A locking system for mechanical joining of floorboards (1) of the type having a
body (30), opposite first and second joint edge portions (4a, 4b) and a balancing
layer (34) on the rear side of the body (30), adjoining floorboards (1, 1') in a mechanically
joined position having their first and second joint edge portions (4a, 4b) joined
at a vertical joint plane (F), said locking system comprising:
a) for vertical joining of the first joint edge portion (4a) of the first floorboard
(1) and the second joint edge portion (4a, 4b) of the adjoining second floorboard
(1') mechanically cooperating means (36, 38) in the form of a tongue groove (36) formed
in the first joint edge portion (4a) and a tongue (38) formed in the second joint
edge portion (4b),
b) for horizontal joining of the first joint edge (4a) of a first floorboard (1) and
the second joint edge portion (4b) of an adjoining floorboard (1') mechanically cooperating
means (6, 8; 14) comprising
a locking groove (14) formed in the underside (3) of said second board (1') and
extending parallel to and at a distance from the vertical joint plane (F) at said
second joint edge portion (4b) and having a downward opening, and
a strip (6) integrally formed with the body (30) of said first floor board (1),
which strip at said first joint edge portion (4a) projects from said vertical joint
plane (F) and at a distance from the joint plane (F) has a locking element (8), which
projects towards a plane containing the upper side (2) of said first floorboard (1)
and which has at least one operative locking surface (10) for coaction with said locking
groove (14), and
the strip (6) forming a horizontal extension of the first joint edge portion (4a)
below the tongue groove (36),
characterised in that the first joint edge portion (4a), within an area (P) defined by the bottom
of the tongue groove (36) and the locking surface (10) of the locking element (8),
is modified with respect to the balancing layer (34).
2. A locking system according to claim 1, wherein the balancing layer (34), within
said area (P) of the first joint edge portion (4a), is lacking or is wholly or partially
removed.
3. A locking system according to claim 1, characterised in that the balancing layer (34) within said area (P) of the first joint edge portion
(4a) is modified with respect to its properties, compared with the properties of the
balancing layer within the remaining parts of the floorboard (1).
4. A locking system according to any one of the preceding claims, wherein essentially
the entire area (P) is modified with respect to the balancing layer.
5. A locking system according to any one of claims 1-2, wherein said area (P) is modified
with respect to the balancing layer (34) across only a part of its horizontal extent.
6. A locking system according to claim 5, wherein said area (P) is modified with respect
to the balancing layer (34) across more than half of its horizontal extent.
7. A locking system according to any one of the preceding claims, wherein the first
joint edge portion (4a) is modified with respect to the balancing layer (34) also
in a second area (L) under the locking element (8).
8. A locking system according to any one of claims 1-6, wherein the first joint edge
portion (4a) exhibits a non-modified balancing layer (34') in a second area (L) under
the locking element (8).
9. A locking system according to any one of the preceding claims, wherein said modification
refers to an alteration of the thickness of the balancing layer (34).
10. A locking system according to any one of the preceding claims, wherein said area
(P) has no balancing layer at all across at least part of its horizontal extent.
11. A locking system according to any one of the preceding claims, wherein said area,
across its whole horizontal extent or a part thereof, exhibits a balancing layer (34)
with reduced thickness.
12. A locking system according to any one of the preceding claims, wherein the first
joint edge portion (4a) is modified within said area (P) with respect to the material
composition of the balancing layer (34).
13. A locking system according to any one of the preceding claims, wherein the first
joint edge portion (4a) within said area (P) is modified with respect to the material
properties of the balancing layer (34).
14. A locking system according to any one of the preceding claims, wherein the locking
system is designed in such a way that the tongue (38) is anglable into the tongue
groove (36) and the locking element is insertable into the locking groove (14) by
means of a mutual angular movement of the first and the second floorboard (1, 1')
while maintaining contact between joint edge surface portions (41, 42) of the floorboards
close to the boundary line between the joint plane (F) and the upper side (2) of the
floorboards.
15. A locking system according to any one of the preceding claims, wherein the floorboards
(1, 1') on the upper side (2) of the body (30) have a surface layer (32) which coacts
with the balancing layer (34).
16. A locking system according to any one of the preceding claims, wherein the tongue
groove (36) has a tongue groove depth (G) which is less than 0.4 times the thickness
(T) of the board (1), and wherein the strip (6) has a width (W) which is less than
1.3 times the thickness (T) of the board (1).
17. A locking system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) has a vertical extent (LH) which is at least
0.1 times the thickness (T) of the board.
18. A locking system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) is inclined relative to the horizontal plane
at an angle (A) exceeding 45°.
19. A locking system according to any one of the preceding claims, wherein the tongue
groove '(36) exhibits an outer part (G2) with a vertical height and an inner, narrower
part (G1) with a vertical height whose average value across the horizontal extent
of the inner part (G1) is less than 0.8 times the vertical height of the outer part
(G2) .
20. A locking system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) has a vertical extent (LH) which is less than
0.2 times the thickness (T) of the board.
21. A locking system according to any one of the preceding claims, wherein the strip
(6), across at least half of the part (P) of the strip which in the horizontal direction
is located between the locking surface (10) and the joint edge of the other board
(1), exhibits a strip thickness (SH) which is less than 0.25 times the thickness (T)
of the board.
22. A floorboard provided with a locking system according to any one of claims 1-21.
23. A floorboard according to claim 22, which is mechanically joinable to adjoining
boards along all four sides by means of a strip-lock system.
24. A method for making mechanically joinable floorboards (1) comprising the steps
of
forming each floorboard (1) from a body (30),
providing the rear side of the body (30) with a balancing layer (34),
forming the floorboard with first and second joint edge portions (4a, 4b),
forming said first joint edge portion (4a) with
a joint edge surface portion (41) extending from the upper side (2) of the floorboard
and defining a joint plane (F) along said first joint edge portion (4a),
a tongue groove (36) which extends into the body from said joint plane (F),
a strip (6) formed from the body (30) and projecting from said joint plane (F)
and supporting at a distance from this joint plane an upwardly projecting locking
element (8) with a locking surface (10) which faces said joint plane (F),
forming said second joint edge portion (4b) with
a second joint edge surface portion (42) projecting from the upper side (2) of
the floorboard and defining a joint plane (F) along said second joint edge portion
(4b),
a tongue projecting from this joint plane for coaction with a tongue groove of
the first joint edge portion (4a) of an adjoining floorboard, and
a locking groove (8) which extends parallel to and at a distance from the joint
plane (F) of said second joint edge portion (4b) and which has a downward opening
and is designed for receiving the locking element (8) and cooperating with said locking
surface (10) of the locking element (8),
characterised by the step of working the balancing layer within an area (P) defined by the bottom
of the tongue groove (36) and the locking surface (10) of the locking element (8).
25. A method according to claim 24, wherein the step of working the balancing layer
(34) comprises machining.
26. A method according to claim 25, wherein the step of machining comprises groove-milling
or slot-forming in said area (P).
27. A method according to claim 24, wherein the step of working the balancing layer
(34) comprises chemical working.
28. A method according to any one of claims 24-27, wherein the step of working the
balancing layer (34) is carried out prior to the step of forming the strip (6) from
the body (30).
29. A method according to any one of claims 24-27, wherein the step of working the
balancing layer (34) is carried out subsequent to the step of forming the strip (6)
from the body (30).
30. A method according to any one of claims 24-29, wherein the step of working the
balancing layer (34) is carried out using the rear side (3) of the board (1) as a
reference surface such that the result of the working of the balancing layer (34)
is independent of any thickness tolerances of the floorboard (1).
31. A method according to any one of claims 24-30, wherein essentially the entire
balancing layer is removed across the entire said area (P) as a result of said working.
32. A method according to any one of claims 24-30, wherein essentially the entire
balancing layer is removed across only a part of said area (P) as a result of said
working.
33. A method according to any one of claims 24-30, wherein the balancing layer (34)
is only partially removed across at least a part (34") of said area (P) as a result
of said working.
34. A method according to any one of claims 24-33, wherein the balancing layer (34)
is worked across at least 50% of said area.
35. A method according to any one of claims 24-33, wherein at least some of the spaces
forming as a result of the removal of the balancing layer (34) are filled at least
partially with material which has properties different from those of the balancing
layer (34).
36. A locking system for mechanical joining of floorboards (1) which have a thickness
(T) and exhibit a body (30), opposite first and second joint edge portions (4a, 4b),
a balancing layer on the rear side of the body (30), adjoining floorboards (1, 1')
in a mechanically joined position having their first and second joint edge portions
(4a 4b) joined at a vertical joint plane (F), and a balancing layer (34) on the rear
side of the body (30), said system comprising
a) for vertical joining of the first joint edge portion (4a) of the first floorboard
(1) and the second joint portion (4a, 4b) of the adjoining second floorboard (1')
mechanically cooperating means (36, 38) in the form of a tongue groove (36) formed
in the first joint edge portion (4a) and a tongue (38) formed in the second joint
edge portion (4b), and
b) for horizontal joining of the first joint edge portion (4a) of a first floorboard
(1) and the second joint edge portion (4a, 4b) of an adjoining second floorboard (1')
mechanically cooperating means (6, 8; 14), which comprise
a locking groove (14) formed in the underside (3) of said second board (1') and
extending parallel to and at a distance from the vertical joint plane (F) at said
second joint edge portion (4) and having a downward opening, and
a strip (6) integrally formed with the body (30)
of said first floorboard (1), said strip projecting at said first joint edge portion
(4a) from said vertical joint plane (F) and at a distance from the joint plane (F)
having a locking element (8), which projects towards a plane containing the upper
side (2) of said first floorboard (1) and which has at least one operative locking
surface (10) for coaction with said locking groove (14), and
the strip (6) forming a horizontal extension of the first joint edge portion (4a)
below the tongue groove (36),
characterised in that the tongue groove depth (G) is less than 0.4 times the thickness (T) of the
board (1), and that the strip width (W) is less than 1.3 times the thickness (T) of
the board (1).
1. A flooring system comprising a plurality of floorboards having a locking system for
mechanical joining of such floorboards (1), the floorboards having a thickness (T)
and exhibiting a body (30), opposite first and second joint edge portions (4a, 4b),
a balancing layer on the rear side of the body (30), adjoining floorboards (1, 1')
in a mechanically joined position having their first and second joint edge portions
(4a 4b) joined at a vertical joint plane (F), and a balancing layer (34) on the rear
side of the body (30), said locking system comprising
a) for vertical joining of the first joint edge portion (4a) of a first floorboard
(1) and the second joint portion (4a, 4b) of an adjoining second floorboard (1') mechanically
cooperating means (36, 38) in the form of a tongue groove (36) formed in the first
joint edge portion (4a) and a tongue (38) formed in the second joint edge portion
(4b), and
b) for horizontal joining of the first joint edge portion (4a) of the first floorboard
(1) and the second joint edge portion (4a, 4b) of the adjoining second floorboard
(1') mechanically cooperating means (6, 8; 14), which comprise
a locking groove (14) formed in the underside (3) of said second board (1') and
extending parallel to and at a distance from the vertical joint plane (F) at said
second joint edge portion (4) and having a downward opening, and
a strip (6) integrally formed with the body (30) of said first floorboard (1),
said strip projecting at said first joint edge portion (4a) from said vertical joint
plane (F) and at a distance from the joint plane (F) having a locking element (8),
which projects towards a plane containing the upper side (2) of said first floorboard
(1) and which has at least one operative locking surface (10) for coaction with said
locking groove (14), and
the strip (6) forming a horizontal extension of the first joint edge portion (4a)
below the tongue groove (36),
characterised in
that the tongue groove depth (G) and/or the width of the tongue is less than 0.4 times
the thickness (T) of the board (1),
that the tongue groove depth (G) is larger than the width of the tongue, and
that the strip width (W) is less than 1.3 times the thickness (T) of the board (1).
2. A flooring system according to claim 1, wherein the tongue groove depth (G) is less
than 0.4 times the thickness (T) of the board (1), and the strip width (W) is less
than 1.3 times the thickness (T) of the board (1).
3. A flooring system according to claim 1 or 2, wherein the width of the tongue is less
than 0.4 times the thickness (T) of the board (1), and the strip width (W) is less
than 1.3 times the thickness (T) of the board (1).
4. A flooring system according to any one of the preceding claims, wherein the locking
system is designed in such a way that the tongue (38) is anglable into the tongue
groove (36) and the locking element is insertable into the locking groove (14) by
means of a mutual angular movement of the first and the second floorboard (1, 1')
while maintaining contact between joint edge surface portions (41, 42) of the floorboards
close to the boundary line between the joint plane (F) and the upper side (2) of the
floorboards.
5. A flooring system according to any one of the preceding claims, wherein the locking
system is designed in such a way that the floorboards are joinable through a snap
action, which is incurred by a horizontal displacement of first and the second floorboards
(1, 1') towards each other, whereby the strip (6) is forced to move downwards as a
direct result of the bringing together of the floorboards and then snaps up and allows
the locking element (8) to enter the locking groove (14).
6. A flooring system according to any one of the preceding claims, wherein the floorboards
(1, 1') on the upper side (2) of the body (30) have a surface layer (32) which coacts
with the balancing layer (34).
7. A flooring system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) has a vertical extent (LH) which is at least
0.1 times the thickness (T) of the board.
8. A flooring system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) is inclined relative to the horizontal plane
at an angle (A) exceeding 45°.
9. A flooring system according to any one of the preceding claims, wherein the tongue
groove (36) exhibits an outer part (G2) with a vertical height and an inner, narrower
part (G1) with a vertical height whose average value across the horizontal extent
of the inner part (G1) is less than 0.8 times the vertical height of the outer part
(G2).
10. A flooring system according to any one of the preceding claims, wherein the locking
surface (10) of the locking element (8) has a vertical extent (LH) which is less than
0.2 times the thickness (T) of the board.
11. A flooring system according to any one of the preceding claims, wherein the strip
(6), across at least half of the part (P) of the strip which in the horizontal direction
is located between the locking surface (10) and the joint edge of the other board
(1), exhibits a strip thickness (SH) which is less than 0.25 times the thickness (T)
of the board.
12. A flooring system according to claim 10, wherein the floorboards are mechanically
joinable to adjoining boards along all four sides by means of said locking system.
13. A flooring system as claimed in any one of the preceding claims, wherein said tongue
(38) has an upper contact surface for interaction with an upper surface of said tongue
groove (36), said upper contact surface being substantially parallel to a principal
plane of said floorboards (1, 1').
14. A flooring system as claimed in any one of the preceding claims, wherein said tongue
(38) has a lower contact surface for interaction with a lower surface of said tongue
groove (36), said lower contact surface being substantially parallel to a principal
plane of said floorboards (1, 1').
15. A flooring system as claimed in any one of claims 1-12, wherein said tongue (38) has
an upper contact surface for interaction with an upper surface of said tongue groove
(36), and a lower contact surface for interaction with a lower surface of said tongue
groove (36), whereby said upper and lower contact surfaces are substantially parallel
to a principal plane of said floorboards (1, 1').
16. A flooring system as claimed in any one of claims 13-15, wherein said upper and/or
lower contact surfaces are substantially less than 0.4 times the thickness (T) of
the board (1).
17. A flooring system as claimed in any one of the preceding claims, wherein the tongue
groove depth (G) and the strip width (W) are so designed as to reduce or eliminate
humidity-related bending of the' strip (6) and/or bending of the strip (6) induced
by a biasing of the balancing layer.